Solvent dewaxing



Patented Aug. 9, 1949 SOLVENT DEWAXING Roy 'r. Edwards, Hollis, andRobert B. Killingsworth, Douglaston, N. Y., assignors to Socony VacuumOil Company, Incorporated, acorporation of New York No Drawing.Application November 22, 1947,

Serial No. 787,622 I 6 Claims. (Cl. 196-18) This invention relates to amethod for separating waxy oils into dissimilar constituents of wax andoil. More particularly, the present invention is concerned with animprovement for separating waxy constituents from wax-bearing petroleumoils with the aid of a selective solvent.

It is well known in the art that waxy constituents can be separated frommineral oils by various methods, all of which have in common the featureof cooling the wax-containing oil to relatively low temperatures tosolidify the waxy constituents and thereafter filtering, centrifuging,or otherwise physically separating the wax from the oilwax slurry. It isalso known in the art that the separation of the wax from wax-bearingoils can be facilitated and diluent materials. Those methods in whichthe diluent used is one tending to exert a preferential solvent actionfor oil over waxy material at low temperatures are commonly known assolvent de-; waxing methods. One widely used version of this methodmakes use of a mixture of an oil solvent such as benzol or toluol and awax anti-solvent such as a ketone, for example, acetone or methyl ethylketone. Other selective solvents which have been used commercially forfacilitating the separation of wax and oil include light naphthas,propane, pentane, hexane, and the like, as well as various acetates,alcohols, andchlorinated hydrocarbons. The chlorinated solvents,although well known for their selectivity in separating wax from oil,have not been widely accepted by the refining industry because of highcost and relative instability. The latter undesirable property leads tothe formation of hydrochloric acid which, in turn, gives rise to aproblem of corrosion.

-A dewaxing process wherein any of the aforementioned solvents areemployed usually requires a temperature of the order of F. or lower toobtain an efiicient separation of waxy constituents from the oil. Otherdifliculties in the processes heretofore employed include changes in theaccelerated by utilizing various ing the solvent-waxy oil mixture, whichheretofore has been a necessary procedural step in dewaxing operations,is hence eliminated by practice of the present invention.

It has been found that fluorinated aromatic hydrocarbons boiling withinthe approximate range of 150 F. to 450 F. have an unusually high solventpower for oil with a comparatively low solvent action for wax. Variousfluorinated aliphatic hydrocarbons, such as dichlorodifiuoromethane andthe like, have this property to a limited extent, but they do notaccomplish the desirable results obtained with the use of fluorinatedaromatic hydrocarbons boiling in the above defined range and, beingextremely volatile, they are not adaptable for use at ambienttemperature.

One of the major factors influencing the suitability and adaptability ofa material for use as a dewaxing or deoiling solvent is its relativesolubility for the waxy constituents and for the oily constituents. Theideal solvent is one which will show a relatively low solubility for thewaxy constituents, will exhibit a relatively high solubility for theoily fractions, and will also remain completely miscible with the oilyconstituents at the temperatures employed for dewaxing. Complete ratioof the constituents of the solvent mixture when the dewaxing operationis carried out in two or more stages.

In accordance with the present invention, there has now been discovereda solvent which may be employed in separating waxy constituents fromwax-bearing oils without necessitating refrigeration of the solvent-waxyoil mixture. It has been found that dewaxing operations can beeffectively carried out at substantially ambient temperature to providean excellent separation between wax and oil. The time and expenseinvolved in coolmiscibility between the solvent and the oilyconstituents is necessary in order to secure a satisfactory separationof the wax crystals from the dewaxing solution.

In addition to having an unusually high solvent power for oil and acomparatively low solvent action for wax, the solvents of this inventionhave the desirable property of permitting an effective separation of waxand oil to take place at substantially room temperature. This unexpectedproperty thus provides a dewaxing or deoiling procedure wherein thecooling step, heretofore essential with the use of conventionalsolvents, may be eliminated. Since refrigeration is a rather costlyoperation, the discovery of a solvent which will precipitate ,wax fromoil at ambient temperature provides a separating medium of considerablvalue.

Representative of the fluorinated aromatic hydrocarbons which arecontemplated for use as solvents in the present process for separatingwax and oil are benzotrifiuoride, xylene hexafiuoride, fiuorobenzene,fluorotoluene, fiuoroxylene, fiuoronaphthalene, and mixtures of two ormore of the foregoing. The list of above mentioned compounds isnot to beconstrued as limiting since other fiuorinated aromatics boiling in therange of F. to 450 F. may also be used. However,

under usual operating conditions, preference is accorded fluorinatedaromatic hydrocarbons with fluorine present in a saturated aliphaticside chain attached to the aromatic nucleus. Benzotrifluoride andmixtures thereof are particularly preferred since this compound isextremely effective in bringing about a separation of oil and wax atambient temperature. A blend of benzotrifluoride and xylene hexafluoridehas, as will tures. Thus, they may be employed in the treatmerit offatty oils and acids such as those derived from vegetable and animalsources.

The desirability of using the present class of dewaxing solvents may beseen fromthe following illustrative examples presented in tabular form,in whichx comparison is made between be shown hereinafter, been found toprovide an solvents of this invention and the conventionally excellentseparation medium. employed blends of benzol and methylethyl Thesolvents of the present invention may be ketone. The procedure followedin these exemployed in either deoiling operations, wherein a amples wasessentially as followsi A wax charge small amount of oil is removed fromlarger was brought into contact with the desired solvent,

amounts of wax, or in dewaxing operations, the ratio of solvent topetrolatum being about 4 wherein minor proportions of wax-are removedto 1. The mixture was then heated toatemperafrom oil solutions.- Theyare suitable for use in ture of 125 F. to insure thorough contactbeoperations conducted over a wide range of temtween the waxy charge andsolvent. The mix-- perature and pressure conditions. In carrying turewas then cooled to the desired filtration temout the separation of waxand oil in accordance perature, precipitating microcrystalline wax, and

with the present invention, the solvent is added the wax was removed byfiltration. The wax cake to the waxy oil and the mixture is heated toasformed was washed once with solvent, removed,

sure complete miscibility of all wax and oil fracand the solventseparated from the cake by evapotions with the solvent. The mixture maythen ration. The resultsobtained under varying conbe cooled to atemperature between about .30 F. ditions of temperature are set forthbelow:

, Table 1 Examples. 1 2 a 4 5 aas er eants? assert, a Benzol. Benwl.

Wax charge, gm. 25;

Solvent/Petrolatum Ratio 4:l

Wash Ratio 1:1..

and about 80? F. While theconventional dewaxing temperatures of fromabout F. to about 30 F. may be used with the solvents of this invention,a particularly desirable feature of the fiuorinated aromatic compoundsemployed herein is that they also permit an efiective separation of thewax and oil at temperatures of from about 30 F. up to about 80 F.,thereby allowing the dewaxing 0r deoiling procedure to be effected atsubstantially room temperature. The exact temperature chosen will bedependent upon the char-' acter of the crystallized wax to be removedand the pour point desired in the dewaxed oil. The

crystallized wax is removed either by filtration or v by centrifuging,while the solvent is removed from" the dewaxed oil fraction bydistillation.

The amount of solventemployed may vary widely and depends upon theparticular oily wax mixture being treated, the solvent employed, and

the characteristics desired in theflnal product.

In general, it ispreferred to employ from one to four volumes of solventper volume of oil being dewaxed.

Undercertain conditions, the solvents of the present inventionmay beemployed in conjunction with various other conventional solvents, suchas ketones, benzol, petroleum, naphtha, lower boiling hydrocarbons, andthe like.

It is also .oontemplated that the solvents of this invention may be usedin the dewaxing of various types of mineral oil stocks .or in thedeoiling of different types of slack waxes and waxy An examination ofthe above data clearly in-- methylethyl ketone was employed at atempera- .ture of 0 F. Approximately the same yields of microcrystallinewaxes of equivalent characteristics were obtained in each of theseexamples. This indicates that the blend of fluorinated aromaticcompounds canbe used to give the same re- F tially lower temperatures.

sults at higher temperatures as are obtained with the benzol-methylethylketone blend at substantion of the results obtained in Example} comparedwith those of Example 4 and the results obtained in Example 3 comparedwith those of Example 5 shows that the solvents or the present inventionas compared with the conventional,

benzol-ketone blends give considerably greater yields of wax when theseparation process is carried out under the same conditions oftemperature.

It is apparent from the above results that the 7 fluorinated aromatichydrocarbon solvents of this A further examinainvention representimproved media for effecting the separation of wax and oil over a widerange of temperature and are particularly applicable in effecting saidseparation under ordinary temperature conditions, thereby eliminatingthe need for carrying out the separation process at low temperatures ofthe order of E, which has heretofore been essential with the use ofconventional solvent blends.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. A process for separating waxy constituents from an oil containing thesame, which comprises admixing the oil with an oil solvent comprising anefiective amount of xylene hexafiuoride.

2. A process for separating waxy material from a mixture of oil and waxymaterial, which comprises mixing said mixture with a solvent comprisingan efiective amount of xylene hexafluoride, maintaining the mixture offeed and solvent at a temperature at which waxy constituents separatefrom the mixture in solid form while the oil remains substantiallycompletely dissolved in the solvent and removing the solidifiedconstituents therefrom.

3. A process for effecting the separation of a mixture of wax and oil,which includes the step of contacting said mixture with xylenehexafluoride.

4. A process for de-oiling a wax, which com- 35 2,152632 prisescontacting an oil-containing wax with an 6 oil solvent containing aneffective amount or xylene hexafiuoride.

5. A process for effecting the separation of a mixture of wax and oil,which comprises contacting said mixture with a solvent comprising aneffective amount of xylene hexafiuoride, heating the mixture of feed andsolvent to a temperature suflicient to dissolve the wax, cooling theresulting mixture to a temperature between about 30 F. and about F.,during which time waxy constituents separate from the mixture in solidform while the oil remains substantially completely dissolved in thesolvent and thereafter removing solidified constituents from themixture.

6. A process for de-oiling a wax, which comprises contacting anoil-containing wax with an oil solvent consisting essentially of xylenehexafiuoride, heating the mixture of feed and solvent to a temperaturesuflicient to dissolve the wax, cooling the resulting mixture to atemperature between about 30 F. and about 80 F., during which time waxyconstituents separate from the mixture in solid form while the oilremains dissolved in the solvent and thereafter removing solidifiedconstituents from the mixture.

ROY T. EDWARDS. ROBERT B. KILLINGSWORTI-I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Terres June 13, 19 9 Number

